The present invention relates to a process for the manufacture of a flowable granulate and to a specific granulate manufactured from epoxy resins and substances having a high specific surface that are insoluble therein.
Polyglycidyl compounds are often used today as a reactive component of curable compositions, for example as hardeners or cross-linking agents in powder coating compositions based on polyesters. Many polyglycidyl compounds are liquid or semi-solid at room temperature or slightly elevated temperature and therefore have only a limited suitability for powder coating applications.
U.S. Pat. No. 5,525,685 describes solid compositions consisting of liquid or semi-solid epoxy resins and solid colloidal condensation polymers of urea or melamine and formaldehyde, which compositions are suitable as hardeners for powder coating compositions. The solidification of liquid epoxy resins requires, however, relatively high quantities of the inert condensation polymer, which results in a relatively low epoxy content in the powder coating composition hardener.
U.S. Pat. No. 5,294,683 describes the preparation of solid solutions by melting and subsequently cooling a mixture of at least one polyglycidyl compound that is solid at room temperature and at least 5% by weight of a polyglycidyl compound that is liquid at room temperature. The solid products so obtained are substantially free of inert components and have a high epoxy content. In that process, the solid products are obtained in the form of flakes that have a tendency to cake when stored for relatively long periods. Before being processed to form powder coating compositions, those flakes are ground to powders by various processes (e.g. by cryo-grinding), there being obtained, however, a material having a high dust content and a broad particle size distribution.
The problem of the present invention was to develop a process for the manufacture of free-flowing granulates of defined particle size and narrow particle size distribution that are stable to storage and have a low dust content.
Granulates having a narrow particle size distribution can generally be manufactured from liquid products, such as solutions or melts, by the process of continuous spray granulation which is described, for example, in U.S. Pat. No. 3,879,855. That process is problematical, however, where the solidification of epoxy resins is concerned. For example, in the case of spray granulation of the solid solutions described in U.S. Pat. No. 5,294,683, an agglomerating, poorly flowing, lumpy material is obtained.
It has now been found that waxy, semi-solid or cohesive (sticky) materials can be solidified by means of spray granulation without any problems to form free-flowing granulates having a low dust content and a narrow particle size distribution by the addition of a small quantity of a substance having a large surface area that is insoluble therein.
The problem of solidifying waxy or sticky substances or mixtures of substances arises especially in certain applications of polymeric or polymerisable substances. Use in powder coating compositions, for example, requires a high dispersibility; in addition, the substance should be in the form of a flowable solid that is stable to storage and has as low a proportion of fine dust as possible.
The present invention accordingly relates to a process for the manufacture of a flowable granulate by means of spray granulation, which process comprises using as starting material a formulation in liquid form comprising
(a) a substance or a mixture of substances that is in the form of a waxy or cohesive solid at room temperature, and
(b) up to 20% by weight, based on the amount of component (a), of a substance having a specific surface  greater than 3 m2/g that is insoluble in component (a).
The process of spray granulation is known to the person skilled in the art from numerous publications, for example from U.S. Pat. No. 3,879,855, European Patent Applications EP-A-0 087 039, EP-A-0 163 836, EP-A-0 332 929, EP-A-0 600 211 and EP-A-0 787 682, or German Offenlegungsschriften DE-A-29 41 637 and DE-A-43 04 809.
Preferably, the spray granulation is carried out as a fluidised-bed process.
In principle, spray granulation for the solidification of liquid or semi-solid epoxy resins can be carried out also as a batch process.
Preferably, however, the process is carried out continuously since, in the continuous process, the desired narrow particle size distribution can be set without any problems. Special preference is given to carrying out the spray granulation as a continuous process with sifting delivery.
By varying the process parameters (residence time, incoming air temperature, product temperature, spray pressure, spray rate, sifter air quantity) granulates having average particle diameters d50 of from 0.1 to 10.0 mm can be produced.
Granulates having average particle diameters d50 of from 0.3 to 5.0 mm, especially from 0.5 to 2.0 mm, are preferred.
The starting materials for the process of the invention are in liquid form, that is to say, they may be solutions, suspensions, emulsions or melts. The liquid products to be sprayed are produced according to customary methods by mixing the constituents and, where applicable, by subsequently heating the resulting mixtures.
When carrying out the process of the invention, the liquid product to be granulated is introduced into the fluidised bed through suitable spray nozzles. One-component nozzles, two-component nozzles or multiple-component nozzles can be used. The use of two-component nozzles, three-component nozzles or higher-multiple-component nozzles is advantageous. Two-component nozzles are especially preferred.
A preferred embodiment is the process of the invention wherein the liquid formulation is a suspension of component (b) in a melt or solution of component (a).
The substance (b) that is insoluble in component (a) can be in the form of a solid or in the form of a suspension in a solvent, for example in water.
When two-component nozzles are used, the liquid formulation to be granulated can be mixed in a pre-mixing zone immediately before being sprayed in. It is also possible for the melt or solution of component (a) and the suspension of component (b) to be supplied separately to a three-component nozzle. In that case, the two components do not mix until sprayed. Another preferred embodiment of the invention, therefore, is a process wherein product introduction is carried out via two-component nozzles with a pre-mixing zone or via three-component nozzles and the liquid formulation is produced immediately before being sprayed in by mixing a melt of the epoxy resin (a) and a suspension of component (b) in an inert solvent.
The process of the invention is used especially in the solidification of semi-solid and waxy or sticky synthetic polymers or corresponding monomers or oligomers, especially thermosetting resins, as component (a).
Examples of such thermosetting resins are phenolic resins, polyurethanes, unsaturated polyester resins and epoxy resins.
Preferably, an epoxy resin or a mixture of epoxy resins is used as component (a) in the process of the invention.
The epoxy resins that are customary in epoxy resin technology can be used as component (a). Examples of epoxy resins are:
I) Polyglycidyl and poly-(xcex2-methylglycidyl) esters, obtainable by reacting a compound having at least two carboxyl groups in the molecule and epichlorohydrin or xcex2-methylepichlorohydrin, respectively. The reaction is advantageously carried out in the presence of bases. Alternatively, such epoxy compounds can also be prepared by esterification with allyl halides and subsequent oxidation.
Aliphatic polycarboxylic acids can be used as the compound having at least two carboxyl groups in the molecule. Examples of such polycarboxylic acids are oxalic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid and dimerised or trimerised linoleic acid. It is also possible, however, to use cycloaliphatic polycarboxylic acids, such as, for example, tetrahydrophthalic acid, 4-methyltetrahydrophthalic acid, hexahydrophthalic acid or 4-methylhexahydrophthalic acid. It is furthermore possible to use aromatic polycarboxylic acids, such as, for example, phthalic acid, isophthalic acid or terephthalic acid.
II) Polyglycidyl or poly-(xcex2-methylglycidyl) ethers, obtainable by reacting a compound having at least two free alcoholic hydroxy groups and/or phenolic hydroxy groups with epichlorohydrin or xcex2-methylepichlorohydrin under alkaline conditions or in the presence of an acidic catalyst with subsequent alkali treatment.
The glycidyl ethers of that type are derived, for example, from acyclic alcohols, e.g. from ethylene glycol, diethylene glycol or higher poly-(oxyethylene) glycols, propane-1,2-diol or poly-(oxypropylene) glycols, propane-1,3-diol, butane-1,4-diol, poly-(oxytetramethylene) glycols, pentane-1,5-diol, hexane-1,6-diol, hexane-2,4,6-triol, glycerol, 1,1,1-trimethylolpropane, pentaerythritol, sorbitol, and from polyepichlorohydrins. Other glycidyl ethers of that type are derived from cycloaliphatic alcohols, such as 1,4-cyclohexanedimethanol, bis(4-hydroxycyclohexyl)methane or 2,2-bis(4-hydroxycyclohexyl)propane, or from alcohols containing aromatic groups and/or further functional groups, such as N,N-bis(2-hydroxyethyl)aniline or p,pxe2x80x2-bis(2-hydroxyethylamino)diphenylmethane. The glycidyl ethers can also be based on mononuclear phenols, such as, for example, resorcinol or hydroquinone, or on polynuclear phenols, such as, for example, bis(4-hydroxyphenyl)methane, 4,4xe2x80x2-dihydroxybiphenyl, bis(4-hydroxyphenyl)sulfone, 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane or 3,3,3xe2x80x2,3xe2x80x2-tetramethyl-5,5xe2x80x2,6,6xe2x80x2-tetrahydroxy-1,1xe2x80x2-spirobisindane. Other suitable hydroxy compounds for the preparation of glycidyl ethers are novolaks, obtainable by condensation of aldehydes, such as formaldehyde, acetaldehyde, chloral or furfuraldehyde, with phenols or bisphenols that are unsubstituted or substituted by chlorine atoms or by C1-C9alkyl groups, such as, for example, phenol, 4-chlorophenol, 2-methylphenol or 4-tert-butylphenol.
III) Poly-(N-glycidyl) compounds, obtainable by dehydrochlorination of the reaction products of epichlorohydrin with amines containing at least two amine hydrogen atoms. Those amines are, for example, aniline, n-butylamine, bis(4-aminophenyl)methane, m-xylylenediamine or bis(4-methylaminophenyl)methane.
The poly-(N-glycidyl) compounds also include, however, triglycidyl isocyanurate, N,Nxe2x80x2-diglycidyl derivatives of cycloalkylene ureas, such as ethylene urea or 1,3-propylene urea, and diglycidyl derivatives of hydantoins, such as of 5,5-dimethylhydantoin.
IV) Poly-(S-glycidyl) compounds, for example di-S-glycidyl derivatives derived from dithiols, such as, for example, ethane-1,2-dithiol or bis(4-mercaptomethylphenyl) ether.
V) Cycloaliphatic epoxy resins, such as, for example, bis(2,3-epoxycyclopentyl) ether, 2,3-epoxycyclopentylglycidyl ether, 1,2-bis(2,3-epoxycyclopentyloxy)ethane or 3,4-epoxycyclohexylmethyl-3xe2x80x2,4xe2x80x2-epoxycyclohexane carboxylate.
It is also possible, however, to use epoxy resins in which the 1,2-epoxy groups are bonded to different hetero atoms or functional groups; those compounds include, for example, the N,N,O-triglycidyl derivative of 4-aminophenols, the glycidyl ether-glycidyl ester of salicylic acid, N-glycidyl-Nxe2x80x2-(2-glycidyloxypropyl)-5,5-dimethylhydantoin and 2-glycidyloxy-1,3-bis(5,5-dimethyl-1-glycidylhydantoin-3-yl)propane.
As component (b) it is possible to use in the process of the invention in principle all compounds that are insoluble in epoxy resins and that have the required high specific surface. Such compounds are known to the person skilled in the art; it is possible to use, for example, adsorbents, such as zeolites, clays (e.g. bentonite), aerosil, micas, or also inorganic or organic pigments.
Preferably, component (b) is a urea-formaldehyde or melamine-formaldehyde condensation polymer.
Urea-formaldehyde condensation polymers are especially preferred. Organic white pigments of that kind are commercially obtainable, for example, under the name Pergopak(copyright).
Preferably, the specific surface of the substances that can be used as component (b) is  greater than 5 m2/g, more preferably  greater than 10 m2/g and most preferably  greater than 15 m2/g.
Methods of determining the specific surface are generally known to the person skilled in the art. The specific surface can be determined, for example, by a modified BET adsorption of nitrogen by the method of Haul and Dumbgen (Chem.-Ing.-Techn. 35, 586 (1963)).
The amount of component (b) in the compositions according to the invention is preferably from 0.1 to 15% by weight, more preferably from 1 to 10% by weight and most preferably from 3 to 7% by weight, based on the amount of component (a).
Preferably, for the process of the invention, the solid solutions known from U.S. Pat. No. 5,294,683 as component (a) are combined with urea-formaldehyde or melamine-formaldehyde condensation polymers as component (b).
The invention further relates, therefore, to a granulate manufactured from a composition comprising
(A) an epoxy resin mixture of at least one polyglycidyl compound that is solid at room temperature and at least 5% by weight, based on the total amount of all the polyglycidyl compounds, of at least one polyglycidyl compound that is liquid at room temperature, at least a portion of the solid polyglycidyl compounds being in the form of a solid mixed phase and the solid mixed phase substantially comprising the total amount of the liquid polyglycidyl compounds as additional component;
(B) up to 20% by weight, based on the amount of component A, of a solid colloidal condensation polymer of urea or melamine and formaldehyde having a specific surface  greater than 3 m2/g.
Its use in the spray granulation process requires the composition of (A) and (B) to be in liquid form. If component (A) is in the form of a solid solution produced by the process described in U.S. Pat. No. 5,294,683, the substance must be melted or dissolved in a suitable solvent before being sprayed. In that case, it is possible to use both inert solvents, such as, for example, acetone, 2-butanone or ethanol, and reactive solvents, such as, for example, epichlorohydrin. It is, however, also possible to use component (A) in the form of a physical mixture of the two polyglycidyl compounds.
As the solid polyglycidyl compound, component (A) preferably comprises a diglycidyl ester or a diglycidyl ether.
Terephthalic acid diglycidyl ester is especially preferred as the solid polyglycidyl compound in component (A).
As the liquid polyglycidyl compound, component (A) preferably comprises a polyglycidyl ester or polyglycidyl ether having at least three glycidyl groups per molecule.
Especially preferred liquid polyglycidyl compounds as constituents of component (A) are trimellitic acid triglycidyl ester, trimesic acid triglycidyl ester and pyromellitic acid tetraglycidyl ester.
The solid colloidal condensation polymers of urea or melamine and formaldehyde according to component (B) of the compositions according to the invention and the preparation thereof are described in Makromol. Chem. 120, 68 (1968) and Makromol. Chem. 149, 1 (1971).
The process of the invention is suitable in general for the manufacture of pulverulent commercial forms, especially for the manufacture of waxy or cohesive substances provided for applications in which the free flowing characteristic, low dust content or an improved dispersibility is important. In the scope of this invention, the expression xe2x80x9chaving a low dust contentxe2x80x9d characterises substances or mixtures of substances in which the proportion of particles having a particle diameter  less than 200 xcexcm is less than 2% by volume.
An important advantage of spray granulation is the optimum heat transfer in the fluidised bed, whereby the formation of threads and sticking together of the particles is prevented. The product yields are very high, especially in the case of the continuous process.
A further advantage is that any solvents present in the starting materials are removed during the spray granulation. Using the process of the invention it is possible to manufacture from originally waxy and cohesive material a free-flowing granulate of definable particle size and narrow particle size distribution that has a low dust content and that is distinguished by a high stability to storage and an improved dispersibility in formulations.
The granulates manufactured by the process of the invention are suitable as cross-linking agents for substances having epoxy-reactive functional groups, e.g. hydroxyl, thiol, amino, amide and, especially, carboxyl groups. Other examples of suitable functional groups are described in Lee/Neville, xe2x80x9cHandbook of Epoxy Resinsxe2x80x9d, MacGraw-Hill, Inc. 1967, Appendix 5-1. For many functional groups the addition of a catalyst can be advantageous. Mixtures of that kind can generally be fully cured at temperatures of from 100 to 250xc2x0 C. and have a variety of uses, e.g. as surface-coating compositions, melt adhesives, casting resins or moulding compositions. Use as cross-linking agents for those epoxy-reactive substances which are solid at room temperature or moderately elevated temperature is preferred.
An especially preferred field of use of the granulates according to the invention is that of powder coating applications.
Those powder coating compositions are preferably based on the polyesters having terminal carboxyl groups that are customarily used in that technology. The polyesters preferably have an acid number of from 10 to 100 and an average molecular weight (weight mean) of from 500 to 10 000, especially up to 2000. Such polyesters are advantageously solid at room temperature and have a glass transition temperature of from 35 to 120xc2x0 C., preferably from 40 to 80xc2x0 C. Suitable polyesters are known, for example, from U.S. Pat. No. 3,397,254.
The invention further relates, therefore, to a powder coating composition comprising a carboxyl-group-containing polyester and a granulate manufactured by the process of the invention.